This invention relates to means for reducing the power consumed in a refrigeration system employing a centrifugal compressor.
In many centrifugal compressors, both the impeller section and the transmission section of the compressor are contained within a single hermetically sealed housing and the two sections interrelated by an impeller drive shaft passing through a wall separating the two sections. Positive and complete sealing of the shaft opening in the wall is never realized in practice. Recognizing that leakage will occur, it is common practice to control the direction of leakage so as to insure that refrigerant will flow into the transmission section rather than oil flowing into the impeller section.
To achieve this result, the transmission chamber is typically vented directly to the evaporator of the refrigeration system thereby placing the transmission at some pressure close to the compressor inlet pressure. The higher pressure generated in the impeller section tends to move refrigerant through the impeller shaft opening into the transmission section thus preventing oil from moving in the opposite direction. The gears of the transmission are thus required to operate in a relatively dense atmosphere of refrigerant vapor. Although gear designs can be optimized to minimize system losses, little can be done, in a mechanical sense, to reduce windage and pumping losses produced by operating in a heavy or dense atmosphere.